Key Points:• ECOSTRESS is a state-of-the-art combination of thermal bands, spatial and temporal resolutions, and measurement accuracy and precision • Data from 82 eddy covariance sites were coalesced concurrently with the first year of ECOSTRESS for Stage 1 validation • Clear-sky ET from ECOSTRESS compared well against a wide range of eddy Abstract The ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) was launched to the International Space Station on 29 June 2018 by the National Aeronautics and Space Administration (NASA). The primary science focus of ECOSTRESS is centered on evapotranspiration (ET), which is produced as Level-3 (L3) latent heat flux (LE) data products. These data are generated from the Level-2 land surface temperature and emissivity product (L2_LSTE), in conjunction with ancillary surface and atmospheric data. Here, we provide the first validation (Stage 1, preliminary) of the global ECOSTRESS clear-sky ET product (L3_ET_PT-JPL, Version 6.0) against LE measurements at 82 eddy covariance sites around the world. Overall, the ECOSTRESS ET product performs well against the site measurements (clear-sky instantaneous/time of overpass: r 2 = 0.88; overall bias = 8%; normalized root-mean-square error, RMSE = 6%). ET uncertainty was generally consistent across climate zones, biome types, and times of day (ECOSTRESS samples the diurnal cycle), though temperate sites are overrepresented. The 70-m-high spatial resolution of ECOSTRESS improved correlations by 85%, and RMSE by 62%, relative to 1-km pixels. This paper serves as a reference for the ECOSTRESS L3 ET accuracy and Stage 1 validation status for subsequent science that follows using these data.
The perjbrmance of a helical screw compressor is influenced more by the internal gas leakages than by any other thermo-juid aspect of its behaviour. Six separate types of leakage path can be identified. Only the cusp blow holes have a constant geometry; every other path has a geometry and resistance toflow which varies (periodically) in a manner unique to it. The pressure difference driving the gas along a leakage path also varies (periodically) and does so in a manner that is not the same for every leakage path. This is quite obviously a complex problem requiring insight in modelling the thermo-fluid behaviour and the solution of a large number of simultaneous equations. The distribution of leakage through the various leakage paths within the machine is important for the improvement of the compressor performance. A method of determining the aggregate leakage through each path individually over a complete compression cycle is required to enable this study to be conducted. The authors have constructed a mathematical model of the complete compressor thermojluid process which is suitable for this purpose, its macropredictions having been verified against measured data derived from a test compressor. The nature of its micropredictions and their verification, that is for each leakage path, are the subject of the paper proposed here. Analytical techniques are proposed and experimental methods are discussed. The influence of diflerent rotational speeds on the leakage is considered. Also discussed is the manner in which the leakage distribution prediction could be used to optimize a compressor design.
Part 1 of this paper describes the origins, principal developments, characteristics, applications and current competitive position of the twin helical screw compressor. It is now the preferred type in a large range of gas and refrigeration applications previously serviced by the larger piston and smaller centrifugal compressors. Its success has been made possible by two crucial developments: (a) a lubricated variant in which one rotor drives the other without timing gears and (b) the introduction of advanced machine tools capable of mass producing reliably a rotor pair of high efficiency and low maintenance. The technical reasons for its (still growing) success over its rivals are explained, as is the competitive challenge presented by the scroll compressor, which is being produced in ever larger sizes. The paper concludes that if the twin helical screw compressor is to maintain/advance its present dominant position, three things are needed: 1. A designer-friendly computerized model of the working process which is comprehensive, accurate and of general application. Part 2, which follows, addresses this issue. 2. A designer-friendly computerized profile design system not limited to predefined geometric forms and having an optimization facility. 3. Faster, more accurate and cheaper manufacturing methods for rotors.
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